In this fourth paper in the Soft Tissue Injury series we cover aspects of soft tissue injury relating to the hip. Our understanding
of injuries to the hip and thigh have increased considerably in recent years, partly through more sophisticated investigation
and partly through much greater investment in sports medicine.1–4 The hip joint is a true “ball and socket” articulation with inherent stability as a consequence of the containment of the
femoral ball within the pelvic socket. The stability of the joint is further enhanced by a strong surrounding capsule and
by a rim of fibrocartilaginous tissue called the acetabular labrum. The capsule thickens at several points to form capsular
ligaments. The labrum effectively deepens the socket. The whole structure is enormously strong, generally resistant to injury
but permitting a significant range of movement befitting the link between the trunk and the lower limbs.

The two halves of the pelvis are linked at the front by the symphysis pubis, and posteriorly by the two sacro-iliac joints
(see fig 1). Neither the sacro-iliac nor the symphysis pubis normally permits movement, although the symphysis may widen and
become painful during pregnancy. All the joints of the pelvis; sacro-iliac, symphysis pubis and hip can suffer dislocations
with or without associated bony injury, although generally do so only with high energy injuries.

Figure 1The bony pelvis viewed from anteriorly.

The condensation of the anterior part of the hip joint capsule is called the iliofemoral ligament (fig 2) and is considerably
thicker than the ischiofemoral ligament, which covers the posterior aspect of the joint. Several layers of muscle overlay
the capsule protecting the joint from direct injury and dynamically stabilise it during activity. Important nerves and vessels
cross the joint and may be injured as a result of both penetrating and non-penetrating injury.